NPB presents an ecologically friendly alternative to 1,1,2-trichloroethane (TCE) for uses such as a cold cleaning solvent. TCE has been identified as having characteristics that are reported to link it to depletion of the earth's ozone layer, thus creating a need for a replacement which will not harm the environment.
Methods of synthesis of NPB are known. Kharasch et al., J. Am. Chem. Soc. 1933, 55, 2532-3, describes addition of hydrogen bromide to propene in the presence of peroxides such as benzoyl peroxide or ascaridole to form NPB. See also Kharasch U.S. Pat. No. 2,058,466. Vaughan et al., J. Org. Chem. 1942, 7, 477-90, describes synthesis, inter alia, of NPB by photohydrobromination of propene in liquid phase. See also Vaughan et al. U.S. Pat. No. 2,307,552. Formation of NPB from vapor phase reaction of hydrogen bromide and propene in the presence of activated carbon catalyst is described in U.S. Pat. No. 2,790,013 to Barnes. U.S. Pat. No. 3,679,759 to Schmerling reports preparation of NPB from concentrated hydrobromic acid and propene at 225° C. and 30-74 atmospheres pressure. British 668,159 reports formation of NPB by passing a mixture of 2 parts by volume of propene and 3 parts of hydrogen bromide gas at the rate of 300 cc per minute into a Siemens-type glass ozonizer.
Some of methods of producing NPB include commercial production by substitution reactions of 1-propanol, by hydrobromination of propene using ozonide catalysts, and by free radical hydrobromination of propene. The latter technology co-produces the secondary bromide isomer, known as isopropyl bromide (IPB). This results in a crude reaction mixture of NPB and IPB, the latter being an undesirable isomer. In certain applications, purities of NPB in excess of 98% are needed which makes it highly desirable to remove IPB from the mixture.
When crude propyl bromide reaction mixtures, formed from a synthesis process employing hydrobromination of propene by hydrogen bromide, are washed with a basic solution to neutralize any excess hydrogen bromide, emulsion problems can result. Such problems are manifested by failure of the alkaline-treated mixture to resolve into two distinct phases, which resolution is necessary for efficient and economical post-synthesis handling of such reaction mixtures.
Therefore a need exists for an NPB synthesis process which provides high yields of NPB in a highly pure state and on an industrial scale, while maintaining safe process conditions and while eliminating undesirable isomers, as in the case of IPB.
A need also exists for a purification process which provides quick and clean phase-cut technology to allow distinct organic/aqueous phase separation for any process wash steps to be employed in an efficient and economical manner. Additionally, a need exists for an NPB composition that maintains its purity and color under typical storage conditions, without the need for additives or stabilizers.
This invention is deemed to enable fulfillment of the foregoing needs and others by the use of the methods and compositions of this invention.